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-   -   Dash 8 Question (https://www.pprune.org/tech-log/386429-dash-8-question.html)

bsal 25th Aug 2009 00:15

Dash 8 Question
 
I've recently noticed that FlyBe Dash 8's leave the speed brakes in the fully deployed position just prior to applying takeoff power, I'm just wondering why this is done.

Gooneyone 25th Aug 2009 00:21

Not too certain of the 400 spoilers, but on the 100 series they are selected to "Flight" (they deploy) just before take-off then they retract with power lever movement fwd. On Landing with weight on wheels and power lever angle they deploy.

G SXTY 25th Aug 2009 00:44

Exactly that, it's a Dash thing. For some reason it has a flight-taxi switch, which when selected to 'taxi' keeps the spoilers retracted. When selected to 'flight', if weight on wheels and power levers are retarded, Dash logic assumes that you are landing and therefore want the spoilers deployed. Once the power levers are advanced, it concludes that you want to go flying and retracts the spoilers.

Don't ask me why, I just drive it . . .

hikoushi 28th Aug 2009 10:14

After the spoilers retract with the power levers advanced for takeoff, in the "flight" mode they remain armed to automatically re-deploy during a rejected takeoff if you retard the power levers again. Only the -100 and -400 use the spoilers on the ground, as far as I know.

adverse-bump 28th Aug 2009 15:30

200 as well i think.

its just the MIGHTY 300 that doesnt

I seem to remember something about 12* power lever angle coming into it somewhere...

hikoushi 28th Aug 2009 19:41

Power lever angle below 12 degrees, Flight / Taxi to "Flight", on the -100 all 3 weight-on-wheels sensors showing on the ground (-400 only needs the main gear WOW) will deploy the roll spoilers in ground mode (and ground spoilers on the -100). The -200s we used to have did not do this; don't know if this applies to all -200s or if there is a mod. We were weight-restricted at certain very short fields in the -200 as a result. Never touched a -300 so couldn't say there.

LimaFoxTango 28th Aug 2009 21:44

Indeed, the -300 didnt have this nifty little feature. I always wondered why it was never installed. I also wondered how effective this feature is performance-wise. Our -100's had the ground spoilers deactivated, so only the roll spoilers would pop up. Also, the Flight/Taxi switch is magnetically latched to the Taxi position. Once the power levers were advanced above 15.5 PLA (according to my notes, not saying that 12 is wrong) the switch would automatically flip up to the Flight position, incase you forgot to do it manually. Happens pretty regularly if you fly a mixed 100/300 fleet.

RVF750 28th Aug 2009 21:49

I used to notice a lot of following traffic mention this over the radio when we lined up at LGW, kind souls, but nobody bothers now they're used to the Q400s there.

I still don't know why the SOP is to manually lift the switch in the line up checks, as it will click up on it's own as you advance the levers and leave the spoilers down as I'm sure it was intended that way, but as said above, I only drive them as I'm told to......

dixi188 31st Aug 2009 10:13

I have not worked on these A/C for 2 years now, but from a MX point of view the extra cycles of operation of the spoilers does seem to cause excessive wear on the linkages between the jacks and the panel. They slam up and down.

I thought that if the switch was allowed to automatically go to the flight position on T.O. then one less cycle per flight would take place.

Also, if a restrictor was put in the hydraulic line then a more gentle operation could be achieved and the wear reduced.


Just my thoughts.


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